As disclosed in Coating Equipment and Processes by George L. Booth, published by Lockwood Publishing, Inc., at pages 75-82, and in Coating and Laminating Machines, by Herbert L. Weiss, published by Converting Technology Company, at pages 165-170, it is well known to use single roll, kiss coaters to apply fluid to the surface of a moving paper web.
U.S. Pat. No. 3,647,525-Dahlgren, at FIG. 1 and at column 5, lines5-11, discloses that it is old to use a doctor blade to wipe off excess fluid from the surface of a single roll kiss coater and to smooth out the film of liquid adhering to the surface of the roll before the film of liquid is rotated into contact with the moving web.
It has been found that the doctored roll coaters as described by Booth, Weiss and Dahlgren are unable to apply certain fluid materials such as emollient fluids in small quantities, in the range of several grams per square meter, with uniformity to the surface of a moving sanitary tissue or towel web. By uniformity, it is not meant that the entire surface of the paper must be coated with the fluid but that there not be large untreated surface areas approximating the shape of an adult human hand. In trying to utilize the doctored roll coating techniques as disclosed by Booth, Weiss and Dahlgren, to apply small quantities of a liquid to a web, it has been found that many large areas were left untreated. Although this problem could be solved by removing less liquid from the applicator roll, this results in more fluid being applied to the web than desired.
Booth, at page 75, states that kiss coaters are normally limited to 500 to 600 while at page 452 he states that the kiss roll can be used at a maximum speed of 1000, it being presumed that in both cases Booth is referring to the web speed in feet per minute. At page 81, Booth states that the speed of the applicator roll varies from 10 per cent to 60 percent of the speed of the web, or in other words, the web is travelling between 1.6 to 10 times the surface speed of the roll.
Both Booth, at page 76, and Weiss, at pages 169 and 170, disclose that fluid strips can be applied to the moving web if lifting fingers or straps are placed between the web and the roll in order to lift portions of the web off of the wetted roll.
U.S. Pat. No. 3,186,377-Schuessler discloses, at column 2, line 70, et seq., the use of a first, notched, doctor blade 22 to wipe excessive fluid from an applicator roll to provide an even distribution of fluid across the peripheral surface of the roll followed by a second blade 23 that is mounted so that its leading edge assumes a wavy configuration to provide a striped pattern of fluid that is applied to the object being coated. Other patents that disclose the use of notched blades are U.S. Pat. No. 3,511,696-Murray which discloses that a notched blade can be used to form stripes of paste which are applied to the surface of a moving web and U.S. Pat. No. 3,565,035-Burgess, et al. which discloses the use of a notched blade 92 for forming beads of glue on a glue roller 70 for application to a supply of labels. It is believed that the prior art patents to Schuessler, Murray and Burgess, et al. are concerned with applying relatively large amounts of material to the surface of the web by means of applicator rollers that have roll surface velocities that are not very different from the speed of the moving web. For example, Burgess, et al. state at column 7, lines 60-61 that the glue roller rotates slightly faster than the transfer roller.
One problem with trying to adapt the single roll kiss coater to solve this problem is that if the web is traveling at speeds of 600 to 2000 feet per minute, and the applicator roll travels at one-tenth the speed of the roll, or 60 to 200 feet per minute (18.3 to 61 meter per minute), many of the emollient fluids will begin to foam which would make the process not commercially feasible.
It is an object of this invention to apply very small amounts of a fluid to the surface of a moving web in a manner that does not leave large patches of untreated web material.
It is another object of this invention to apply an emollient fluid on the order of several grams or less to each square meter of a sanitary paper web.
It is another object of this invention to apply an emollient fluid to a sanitary paper web moving at very high speeds while keeping the surface speed of the applicator roll at a very low speed.